At present, polarizers are produced generally by laminating a protective film such as a cellulose acetate film on at least one side of a polarizing element comprising a stretched and orientated film of polyvinyl alcohol (hereinafter abbreviated as “PVA”) or a derivative thereof containing iodine or a dichroic dye using an aqueous solution containing a PVA resin as an adhesive.
Polarizers having such construction have the defect that the polarizing element and the protective film are apt to separate from each other upon being exposed to high temperature for a long time. Recently, liquid crystal display devices are used in desk electronic calculators, electronic watches or clocks, personal computers, cellular phones and instruments used in automobiles and machines, and are used or stored under severer environmental conditions. Thus, there sometimes occurs the problem that the polarizing element and the protective film separate from each other, particularly, in a high humidity atmosphere to cause deterioration of display quality of the liquid crystal display devices. For improving the strength of adhesives, there is a method of accelerating the reaction of adhesive components, and, in this case, the usable life, so-called, jar life in the state of solution becomes shorter, and hence it is necessary to use two-pack type adhesives. However, one-pack type adhesives have been desired for improving productivity.
Non-Patent Document 1 discloses a general method for improving water resistance of PVA resin-based adhesives.
Patent Document 1 and Patent Document 2 disclose that adhesives comprising a PVA resin, a resin having a maleic anhydride skeleton in the structure and a crosslinking agent are used as wood adhesives.
Patent Document 1: JP-A-49-93446
Patent Document 2: JP-B-03-7230
Non-Patent Document 1: “POVAL” written by Nagano, Yamane and Toyoshima, and published from Polymer Publication Society, on Apr. 1, 1981, pages 256-261